Use of spike tires has been banned by law in Japan for prevention of powder dust pollution resulting from the use of spike tires, and thus winter tires (studless tires) are now used instead of the spike tires in cold regions. Winter tires have been improved in their materials and designs for driving on icy or snowy roads having a rougher surface than that of usual roads. For example, a rubber composition has been proposed in which a diene rubber having excellent low-temperature properties (performance on ice and snow) is added and the amount of a softener is increased for a better softening effect. Here, as the softener, mineral oil is usually used to increase the low-temperature properties.
However, increasing the amount of mineral oil for an increase in low-temperature properties usually leads to a decrease in abrasion resistance. One possible method for solving such a problem is to use aromatic oil instead of mineral oil. In this case, however, the low-temperature properties decrease, thereby making it difficult to achieve sufficient performance on ice and snow. To address this, aromatic oil and silica are used in combination to increase the low-temperature properties without decreasing the abrasion resistance. However, the resulting performance properties remain insufficient. Meanwhile, in addition to the low-temperature properties and abrasion resistance, improved wet grip performance is also desired.
Patent Document 1, for example, discloses a rubber composition for a winter tire which contains large amounts of aromatic oil and silica and is enabled to improve the abrasion resistance, performance on ice and snow, and wet grip performance in a balanced manner. Nevertheless, in recent years, these performance properties have been desired to be further improved.
Patent Document 1: JP 2011-38057 A